Front end whine?!?!

First, this is a great forum with great info!!! I have what seems to be a loud whine coming from the front end. Its a 1998 classic w/ 4x4 and has been a horse since I got it 3 years back. It seems to only do it in gear and only after the engine has warmed up a bit. The whines pitch changes as acceleration increases and decreases. Could it be that cracked exaust manifold I've been hearing so much about? It only started a week ago and has been getting louder and louder. Any help would be gretly appreciated!
Thanks!